Storage control subsystem for managing logical volumes

ABSTRACT

The present invention provides a storage control subsystem that facilitates logical volume access management by a host. Before copying, the host instructs a disk array device to identify the states of target logical volumes and collect information in control memory, whereupon the disk array device reads information in the control memory and reports information relating to the target logical volumes to the host.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application relates to and claims priority from Japanese PatentApplication No. 2003-429793 filed on Dec. 25, 2003, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a storage control subsystem thatcomprises one or more storage devices or a logical volume accessmanagement method for a storage control subsystem. The present inventionalso relates to a storage system that comprises a storage controlsubsystem and a host that is connected to the storage control subsystem.

2. Description of the Related Art

For example, in a business-critical storage system that handles a largevolume of data, data is managed by using a storage control subsystemthat is formed separately from the host computer (hereinafter referredto simply as the ‘host’) This storage control subsystem is also known asa disk array device, for example, and is a RAID (Redundant Array ofIndependent Inexpensive Disks) system that is constituted by arranging amultiplicity of disk-type storage devices in the form of an array.

As an example of a storage system, a technology is known (JapanesePatent Application Laid-Open No. 2001-195201) for collectively changing,with respect to a plurality of volume pairs that are establishedextending over disk devices controlled by a plurality of disk controldevices, the states of all the volume pairs by means of a single statechange request from an upper layer host or operating panel or anevent-driven state change request that is generated within a single diskcontrol device, irrespective of the number of installed disk controldevices, disk devices, and so forth.

Further, in a storage control subsystem, for example, data is copiedfrom a first logical volume to a second logical volume that forms a pair(hereinafter the first logical volume that constitutes the copy sourcewill be called the ‘regular volume’, while the second logical volumeconstituting the copy destination will be called the ‘subvolume’). Inthis case, in order to perform copying to the subvolume normally, thesubvolume must enter an offline state in which same is not connected toany host. This is because, when data is copied to a subvolume that is inan online state, other data is written from the host to the subvolumeduring the copying process and hence there is the risk that the data inthe subvolume will not be the same as the data in the regular volume.

A method of preventing this risk that may be considered is one in whichdata is not copied to the subvolume when the subvolume is in an onlinestate.

However, accordingly, when a plurality of regular volumes constitute asingle copy source, a plurality of subvolumes constitute a single copydestination, and copying is performed with respect to this plurality ofsubvolumes, for example, even if just one of the plurality of subvolumesis in an online state, although copying may be performed normally to theother subvolumes in an offline state, copying to subvolumes in an onlinestate is not executed, and therefore data integrity cannot be preservedbetween the plurality of regular volumes (the copy source) and theplurality of subvolumes (the copy destination).

In order to prevent this situation from arising, before data in aregular volume constituting the target is copied, a subvolume that ispaired with this regular volume must enter an offline state. In thiscase, if the subvolume is connected to at least one host, the user mustfind the connection-destination hosts of the subvolume individually. Inorder to find the connection destination hosts, for example, a firstuser of a first host that outputs a copy command must consult, bytelephone or otherwise, second users of a plurality of second hosts thatare possibly connected to the subvolume, with regard to which logicalvolume these second hosts are connected to. Then, once theconnection-destination second hosts are known, the second user mustrender the subvolume offline by breaking the connection of the secondhosts with the subvolume.

Likewise, when the subvolume is in the online state, normal copyingcannot be executed, and processing that is troublesome for the user isrequired in order to change the online state of the subvolume to theoffline state. This process becomes increasingly difficult as the numberof subvolume connection-destination hosts increases.

SUMMARY OF THE INVENTION

Accordingly, the present invention achieves at least any of thefollowing objects:

(1) The provision of a storage control subsystem in which accessmanagement of logical volumes by a host is straightforward.

(2) The provision of a storage control subsystem that is highly reliablewith respect to data backups.

(3) The provision of a storage control subsystem that has a functionenabling path cancellation through access by a host that is not directlyconnected, such as a host connected via another storage device, forexample.

A further object of the present invention is the backing up of data froma regular volume to a subvolume, that is, to allow data to be backed upnormally to a database constituted by a plurality of subvolumes, forexample.

Yet another object of the present invention is to convert a subvolume inan online state to an offline state easily.

Further objects of the present invention will be readily apparent fromthe following description.

The storage system according to one aspect of the present invention is astorage system comprising one or more host devices, and a storagecontrol subsystem connected to the one or more host devices. The storagecontrol subsystem comprises a channel control unit that controlscommunications with the connected host device(s); a plurality of logicalvolumes prepared on one or more physical storage devices; a disk controlunit that controls the plurality of logical volumes; and control memory.Recorded in the control memory for each of the plurality of logicalvolumes is volume discrimination information, ON/OFF informationindicating whether an online state exists, and, in the event of anonline state, path group information with regard to which host device(s)the subvolume is connected to. The storage control subsystem (channelcontrol unit, for example) is such that, as a result of receiving aspecific command from a certain host device, the channel control unitperforms, before a target regular volume and target subvolume among theplurality of volumes are paired and data in the target regular volume iscopied to the target subvolume, a first examination of whether thetarget subvolume is in an online state on the basis of ON/OFFinformation on the target subvolume, and, when, as a result of thisfirst examination, the target subvolume is known to be in an onlinestate, the channel control unit performs a second examination withregard to which separate host device the target subvolume is connectedto on the basis of path group information on the target subvolume; andthe result of the second examination is sent from the channel controlunit to the certain host device. The host device displays the secondexamination result (discrimination information for the host connected tothe target subvolume, for example). Further, the storage controlsubsystem may send the first examination result to the certain hostdevice or may send the second examination result without sending thefirst examination result. Further, the main body that judges whether thetarget subvolume is in the online state may be the storage controlsubsystem that acquires the first examination result, the certain hostdevice that received the first examination result, or may be the userviewing the first examination result displayed on the certain hostdevice.

The storage control subsystem according to another aspect of the presentinvention comprises a channel control unit that controls communicationswith the connected host device(s); a plurality of logical volumesprepared on one or more physical storage devices; a disk control unitthat controls the plurality of logical volumes; and control memory.Volume discrimination information, ON/OFF information indicating whetheran online state exists, and, in the event of an online state, path groupinformation with regard to which host device the subvolume is connectedto are recorded in the control memory for each of the plurality oflogical volumes by predetermined components of the storage controlsubsystem (the channel control unit and/or device control unit, forexample). The storage control subsystem is such that, as a result ofreceiving a specific command from the host device, the channel controlunit performs, before a target regular volume and target subvolume amongthe plurality of volumes are paired and data in the target regularvolume is copied to the target subvolume, a first examination of whetherthe target subvolume is in an online state on the basis of ON/OFFinformation on the target subvolume, and, when, as a result of thisfirst examination, the target subvolume is known to be in an onlinestate, the channel control unit performs a second examination withregard to which separate host device the target subvolume is connectedto on the basis of path group information on the target subvolume; andthe result of the second examination is sent from the channel controlunit to the certain host device.

The method according to a further other aspect of the present inventionis a method for controlling the storage of data in each of a pluralityof logical volumes prepared on one or more physical storage devices,comprising the steps of: recording, in control memory for each of theplurality of logical volumes, volume discrimination information, ON/OFFinformation expressing whether or not each volume is in an online state,and path group information with regard to which host device a subvolumeis connected to if in the online state; receiving a specific commandfrom the host device; performing a first examination of whether a targetsubvolume is in an online state based on the ON/OFF information on thetarget subvolume before a target regular volume and the target subvolumeamong the plurality of volumes are paired and data in the target regularvolume is copied to the target subvolume; performing a secondexamination with regard to which separate host device the targetsubvolume is connected to based on path group information on the targetsubvolume when, as a result of the first examination, it is clear thatthe target subvolume is in the online state; and sending the result ofthe second examination to the host device.

With the present invention, the user of a certain host device can easilyfind out which host device(s) the target subvolume is online with,thereby alleviating the burden on the user bringing the volumes offline.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the overall constitution of a storagesystem pertaining to an embodiment of the present invention;

FIG. 2 shows an examination command and setting cancellation commandthat are issued by an AP2 of a host 1;

FIG. 3 shows control tables that are generated by a channel control unit4;

FIG. 4 shows an outline of a first processing flow executed when the AP2issues a copy command;

FIG. 5 shows an outline of a second processing flow executed when theAP2 issues a copy command;

FIG. 6 shows an outline of a third processing flow executed when the AP2issues a copy command;

FIG. 7 shows an outline of a fourth processing flow executed when theAP2 issues a copy command;

FIG. 8 shows an example of a priority table 13 to which tape recordingmedia discrimination information has been added;

FIG. 9 is a flowchart for the processing that is executed when a secondexamination command for receiving the provision of a path groupinformation control table 15 is issued;

FIG. 10 is a flowchart for the processing that is executed when asetting cancellation command 13 for changing the subvolume from anonline state to an offline state is issued;

FIG. 11 shows the operational flow of a disk array device 11 of a fourthembodiment example of one embodiment of the present invention;

FIG. 12 shows a sequence of commands between the host 1 and disk arraydevice 11 in the processing flow illustrated in FIG. 4;

FIG. 13 shows a sequence of commands between the host 1 and disk arraydevice 11 for the processing flow illustrated in FIG. 5;

FIG. 14 shows a sequence of commands between the host 1, disk arraydevice 11, and a separate disk array device 11A for the processing flowillustrated in FIG. 6;

FIG. 15 shows a sequence of commands between the host 1, disk arraydevice 11, and a separate disk array device 11A for the processing flowillustrated in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described hereinbelowwith reference to the drawings.

FIG. 1 shows the overall constitution of a storage system pertaining toan embodiment of the present invention.

This storage system comprises a disk array device 11 (RAID, forexample), and one or more host systems 1 (hereinafter referred to simplyas ‘host 1’) connected to the disk array device. Here, the disk arraydevice 11 connected to the host 1 may be connected to another disk arraydevice, a plurality of disk array devices 11 may be connected to asingle host 1, or a plurality of hosts 1 may be connected to a singledisk array device.

The host 1 is a personal computer, a workstation, or the like, forexample, and is a computer system comprising, as hardware resources, aCPU (Central Processing Unit), nonvolatile and/or volatile memory (ROMor RAM, for example), and a hard disk, or the like. A variety offunctions may be implemented by the CPU of the host 1 reading andrunning various programs. The host 1 is connected to the disk arraydevice 11 via a communication network such as a LAN (Local Area Network)or SAN (Storage Area Network), or the like, for example.

As shown in FIG. 1, the host 1 comprises one or a plurality ofapplication programs (hereinafter called ‘AP’) 2, and an operatingsystem (called ‘OS’ hereinafter) 3. The AP2 issues a variety ofcommands, such as a command to form a volume pair in which a firstlogical volume is a regular volume and a second logical volume is asubvolume and then copy data in the regular volume to the subvolume, tothe disk array device 11 via the OS3. Further, the AP2 issues an I/Orequest, which contains a command type (a read request or write request,for example), and a LUN for a logical volume that is a read data readingdestination or a write data storage destination, to the disk arraydevice 11 via the OS3.

The disk array device 11 comprises one or more physical disk groups 9having a plurality of disk-type storage devices arranged in the form ofan array, and a plurality of logical volumes (Logical Units) 10, whichare logical storage regions, are established in a physical storageregion provided by these physical disk groups 9. The disk array device11 comprises a channel control unit 4, cache memory 5, control memory 7,a disk control unit 8, and a switching control unit 6.

The channel control unit 4 controls communication with the connectiondestination host 1 and comprises one or a plurality of channel adaptersets (not shown). Each channel adapter set contains a plurality ofchannel adapters (typically two) connected to one or more host(s) 1.These adapters are constituted in substantially the same way.Accordingly, for example, when the host 1 has been unable to access alogical volume 10 via one channel adapter, access is gained to the samelogical volume 10 via the other channel adapter. Each channel adaptercan be constituted by a hardware circuit, software, or a combinationthereof, and data communications between the disk array device 11 andhost 1 are performed. Mounted in the channel adapter are one or moremicroprocessors (not shown) (hereinafter called ‘channel processors’)connected to one or more hosts 1, a microprocessor adapter (not shown)(hereinafter abbreviated to ‘MPA’) connected to the control memory 7,and a data transfer adapter (not shown) (hereinafter abbreviated to‘DTA’) connected to the cache memory 5. When a channel processor sendsand receives control information (messages to and from the processor,for example) to and from an external microprocessor (more specifically,a microprocessor (not shown) on a disk adapter (described later)),control information is sent and received via the MPA. Further, when datais written from the host 1 to the logical volume 10 (hereinafter thiswritten data will be called ‘write data’), and when data read from thelogical volume 10 (hereinafter this read data will be called ‘readdata’) is output from the disk array device 11 to the host 1, the writedata and read data pass through the DTA. For example, each channelprocessor performs poling of predetermined storage regions of thecontrol memory 7 to acquire control information via the MPA, storesvarious commands received from the host 1 in the control memory 7, readsread data stored in the cache memory 5 and sends this data to the host1, and stores write data received from the host 1 in the cache memory 5.

The cache memory 5 is volatile or nonvolatile memory. Write data that istransferred from a channel adapter to a disk adapter of a subsequentlydescribed disk adapter set, and read data that is transferred from thedisk adapter to the channel adapter are temporarily stored in the cachememory 5.

The control memory 7 is nonvolatile or volatile memory that is shared bythe channel control unit 4 and disk control unit 8.

The disk control unit 8 controls each physical disk group 9 andcomprises a disk adapter set (not shown) that is prepared for eachphysical disk group 9. A disk adapter set comprises a plurality of diskadapters (typically two). Each disk adapter comprises one or a pluralityof microprocessors (not shown) (hereinafter called ‘disk processors’)and reads or writes data to the logical volume 10 that has the logicalvolume number (abbreviated as ‘LUN’ hereinafter) designated by the host1, by means of the disk processor processing (the logical volume 10 mayalso be discriminated by a code other than a LUN).

The switching control unit 6 can be constituted as a high-speed pathsuch as an ultrafast crossbar switch or the like that performs a datatransmission by means of a high-speed switching operation, for example.The switching control unit 6 communicably connects the channel controlunit 4 (channel adapters), the disk control unit 8 (disk adapters), thecontrol memory 7, and the cache memory 5 to one another. The transfer ofdata or commands between these channel adapters, disk adapters, controlmemory 7, and cache memory 5 is performed via the switching control unit6.

An outline of the disk array device 11 pertaining to this embodiment wasprovided above. The disk array device 11 receives an I/O request fromthe AP2 of the host 1 and executes processing based on the content ofthis I/O request.

An outline of the processing flow of the I/O request of the disk arraydevice 11 will be provided below. Further, in this description, a casewhere the issued I/O request indicates a read request and a case where awrite request is indicated will be described separately. This I/Orequest contains the LUN of the logical volume constituting a read-datareading destination or a write data storage destination.

(1) When the I/O Request Indicates a Read Request.

The channel control unit 4 receives the I/O request issued by the host 1and determines whether the data to be read as per the I/O request (thatis, the read data) exists in a predetermined storage region(predetermined cache slot) of the cache memory 5.

When the result of this determination is affirmative, that is, when theread data exists in the predetermined cache slot (in the case of a cachehit), the channel control unit 4 acquires the read data from thepredetermined cache slot and sends this read data to the host 1.

On the other hand, when the result of this determination is negative,that is, when the read data do not exist in the predetermined cache slot(in the case of a cache miss), the channel control unit 4 stores, in thecontrol memory 7, control information for instructing that read data inthe logical volume (hereinafter called the ‘target volume’) 10 to whichthe LUN included in the I/O request has been allocated be read to apredetermined cache slot temporarily. As a result of the disk controlunit 8 reading the control information, read data is read from thetarget volume 10 and stored in the predetermined cache slot by the diskcontrol unit 8. Thereafter, the channel control unit 4 acquires the readdata from the cache memory 5 and sends this data to the host 1.

(2) When the I/O Request Indicates a Write Request.

The channel control unit 4 receives an I/O request containing write datafrom the host 1 and determines whether data exists in a predeterminedcache slot in the cache memory 5.

When the result of this determination is affirmative, that is, when thedata exists in the predetermined cache slot (in the case of a cachehit), the channel control unit 4 overwrites data in the predeterminedcache slot with the write data contained in the I/O request.

On the other hand, when the result of this determination is negative,that is, when the data does not exist in the predetermined cache slot(in the case of a cache miss), the channel control unit 4 stores, in thecontrol memory 7, control information for instructing that data be readfrom the target volume 10 and temporarily stored in the predeterminedcache slot. Upon reading the control information, the disk control unit8 reads data from the target volume 10 and stores this data in thepredetermined cache slot. The channel control unit 4 overwrites writedata contained in the received I/O request with the data stored in thepredetermined cache slot.

Thus, this write request ends when write data has been written to thecache memory 5, and hence a completion report is sent back to the host 1by the disk array device 11. Generally speaking, this data is notreflected in the target volume 10 at the moment the write data iswritten to the cache memory 5. Rather, write data is read from the cachememory 5 and then written to the target volume 10 by the disk controlunit 8.

An outline of the storage system pertaining to this embodiment wasprovided above. In this storage system, the disk control unit 8 and eachphysical disk group 9 may be directly connected, or indirectly connectedvia a network, for example. The physical disk groups 9 and disk controlunit 8 may also be formed integrally. Further, one logical volume 10 maybe allocated to each channel adapter of the channel control unit 4, orone logical volume 10 may be allocated by a plurality of channeladapters. One logical volume 10 may also be shared by a plurality ofchannel adapters. In addition, a separate disk array device 11A may beconnected to the disk array device 11 as described subsequently. In thiscase, for example, a regular volume that exists in the disk array device11 and a subvolume that exists in the separate disk array device 11A arepaired such that the host 1 connected to the disk array device 11 mayaccess the subvolume in the separate disk array device 11A via the diskarray device 11.

The principal parts of the system pertaining to this embodiment will bedescribed in detail below.

In this embodiment, a plurality of regular volumes constitute one copysource CU (Control Unit: a unit constituting an aggregate of a pluralityof logical volumes 10), while a plurality of subvolumes constitute onecopy destination CU. Typically, the number of regular volumesconstituting a copy source CU and the number of subvolumes constitutinga copy destination CU are the same, and a plurality of volume pairs eachconstituted by one regular volume and one subvolume are individuallyformed. Therefore, after each of the regular volumes in the copy sourceCU has been paired with one of more subvolumes in a copy destination CU,data is copied from the copy source CU to the copy destination CU.

Although not illustrated, a CU management table in which discriminationinformation for each CU (CU numbers, for example), and the LUN of eachlogical volume contained in these CUs appear, is stored in the controlmemory 7.

Furthermore, a plurality of control memory address information itemsthat correspond with a plurality of LUN (logical volume numbers) areprepared in the control memory 7 and a LU control table (not shown)corresponding with each LUN is prepared in the locations indicated byeach control memory address information item. In each LU control table,a variety of information relating to the corresponding logical volume10, such as ON/OFF information indicating an online state or offlinestate (a single bit that is ‘0’ or ‘1’, for example), discriminationinformation on each connected host connected to the logical volume (thename, for example), discrimination information for each logical pathlinking each host with the logical volume (the logical path number, forexample), and information indicating whether this path is online, forexample, are registered by the channel control unit 4 and/or the diskcontrol unit 8. Further, a logical path is a path formed logicallywithin a physical path.

The AP2 of the host 1 sends, to the disk array device 11, a copy command(a command to form respective volume pairs consisting of each regularvolume in the copy source CU and each subvolume in the copy destinationCU, and to copy data from the copy source CU to the copy destinationCU), or a recopy command (a command to form each volume pair once againafter each volume pair has been cancelled and then copy data in the copysource CU (only updated data, for example) to the copy destination CU,or the like, in accordance with user operations. Before sending thiscopy command, recopy command, or the like, the AP2 is able to send anexamination command allowing the disk array device 11 to inquire whetherall the subvolumes in the copy destination CU are in an offline state.Further, the AP2 is also able to send an examination command allowingthe disk array device 11 to inquire which separate host(s) 1 subvolumesdesignated by the user are connected to. In addition, the AP2 is alsoable to send a setting cancellation command (described later) tocompulsorily convert a subvolume in an online state into an offlinestate.

FIG. 2 shows an examination command and setting cancellation commandthat are issued by the AP2 of the host 1.

The examination command 12 is a command that causes the disk arraydevice 11 to execute an examination that is executed in accordance withthe content of the command 12 by the channel control unit 4 thatreceives the command 12. The examination command 12 contains anexamination control flag and examination target information.

An ‘examination control flag’ is information indicating which disk arraydevice the command is issued to. More specifically, for example, this isa code indicating whether the host 1 accesses the connection-destinationdisk array device 11 or accesses one or more separate disk array devicesconnected to the disk array device 11. Here, a separate disk arraydevice is a disk array device connected to the disk array device 11 fordata recovery, data backups, and so forth, for example (naturally, theconnection object is not limited to this disk array device). When a codeindicating ‘within unit’ is contained in the examination control flag,this signifies that a command is issued to the connection-destinationdisk array device 11 of the host 1 and an examination is executed by thedevice 11 in accordance with this command. When a code indicating‘separate unit’ is contained in the examination control flag, thissignifies that a command is sent to a separate disk array device andthat an examination is executed by the separate disk array device inaccordance with this command. Further, when there is a plurality ofseparate disk array devices, discrimination information on the separatedisk array device is contained in the examination control flag, and thusa separate disk array device constituting a command issue destinationmay be discriminated by the connection-destination disk array device 11by means of this discrimination information.

‘Examination target information’ includes parameter information forconfirming at what location the channel control unit 4 receiving theexamination command 12 may access the control memory 7.

More specifically, for example, when the examination command 12 forobtaining online information for all the logical volumes 10 contained ina certain CU (information indicating whether the logical volumes 10 areonline or offline by means of a bitmap of ‘0’ or ‘1’ for each LUN), theexamination target information contains codes signifying ‘a plurality ofvolumes’ and CU discrimination information (in addition to or instead ofthe CU discrimination information, the examination target informationmay contain a plurality of LUN corresponding with the plurality oflogical volumes). In such a case, the channel control unit 4 is able tospecify a plurality of LUN corresponding with the CU that has the CUdiscrimination information by using this CU discrimination informationto reference the control memory 7, and is able to reference a pluralityof LU control tables corresponding with the specified plurality of LUN.

Further, for example, when the examination command 12 is for obtainingpath group information on a certain logical volume 10, for example, theexamination target information contains codes signifying a ‘singlevolume’ and the LUN of the logical volume 10 that is the target. Here,the channel control unit 4 is able to reference the LU control tablecorresponding with the LUN.

The setting cancellation command 13 is a command for canceling certainsettings for the disk array device that is the command issuedestination. The setting cancellation command 13 contains a cancellationcontrol flag, cancellation target information, and a clear instruction.

A ‘cancellation control flag’ is the same as the examination controlflag contained in the examination command 12.

‘Cancellation target information’ is the same as the examination targetinformation contained in the examination command 12. For this reason,the channel control unit 4 that receives the setting cancellationcommand 13 is able to specify one or a plurality of target LUN byreferencing cancellation target information and is able to access andreference the LU control table corresponding with the specified LUN.

A ‘clear instruction’ is a code signifying the cancellation of certainsettings of the LU control table specified from the cancellation targetinformation. More specifically, the cancellation control flag signifies‘within unit’, for example, and, when the cancellation targetinformation contains the LUN of a certain single logical volume 10, theclear instruction signifies the cancellation of the online state of thelogical volume 10. The channel control unit 4, which has received thesetting cancellation command 13 that includes this clear instructionchanges the ON/OFF information that is written in the LU control tablecorresponding with the specified LUN from an online state ‘0’ to anoffline state ‘1’.

The above examination command 12, setting cancellation command 13, orthe like, is issued by the AP2 of the host 1 and reaches the channelcontrol unit 4 of the disk array device 11. When the received command isan examination command 12 and executes processing in accordance withthis examination command 12, the channel control unit 4 generates acontrol table (that is, examination result information) such as thatbelow by extracting the information required from the LU control tableof the control memory 7, and sends this control table to the host 1,which is the source of the examination command 12.

FIG. 3 shows the generated control tables.

The control table generated by the disk array device 11 (including theearlier-mentioned separate disk array device) includes an onlineinformation control table 14 and a path group information control table15. After being generated, the control tables 14 and 15 are sent to thehost 1.

The online information control table 14 is generated in CU units. Thenumber of online volumes, first target information, an ON/OFF list, andso forth, are recorded in the online information control table 14 ofeach CU.

The ‘number of online volumes’ is the number of logical volumes in anonline state that are contained in the target CU. The user is thus ableto identify which of the plurality of volumes constituting the target CUis in an online state by referring to the number of online volumes.

‘First target information’ is address information relating to a groupcontaining the logical volumes contained in the target CU. This addressinformation contains, for example, the SSID (Sub System ID: ID of eachsubunit produced by further logical division of the CU into a plurality)of the target CU, the product number of the disk array device with eachvolume in the target CU, the CU number of the target CU, and so forth.The user is able to identify the address information relating to thegroup with each logical volume in the target CU by referencing thisfirst target information.

The ‘ON/OFF list’ is a list that indicates a plurality of logicaladdresses that correspond with a plurality of logical volumes present inthe target CU (a bit map showing a ‘0’ if the corresponding logicalvolume is in an online state and a ‘1’ if this volume is in an offlinestate). More specifically, for example, when 256 logical volumes 10exist in the target CU, for example, the ON/OFF list is 32-byteinformation with 256 one-bit information items corresponding with the256 logical volumes 10. The user is able to identify whether a volume inan online state exists in the target CU by referencing this ON/OFF list.

The path group information control table 15 is generated in logicalvolume units. The path group information control table 15 of eachlogical volume contains the number of online paths, second targetinformation, path group information, and so forth.

‘The number of online paths’ is information indicating how may pathshave been set in the target volume. The channel control unit 4references the LU control table of the target volume (table registeredin the control memory 7), captures the logical paths in an online state,and registers the number of captured logical paths as the number ofonline paths. The user is thus able to identify the number of hostsconnected to the target volume by referencing the number of onlinepaths.

‘Second target information’ is information arrived at by adding addressinformation (the LUN and/or path to the target volume, for example)relating to the target volume itself to the first target informationcontained in the volume online information control table 14.

‘Path group information’ indicates information relating to a logicalpath between the target volume and a host connected to the targetvolume. More specifically, for example, ‘path group information’ denotesthe number of a logical path set in the target volume, and path groupattribute information. For example, the logical path number is thenumber of an online logical path, and, more specifically, whether thelogical path is online or not is expressed by the binary digits 1 and 0(0: online, an 1: offline), and these bits are expressed in the formatof a bitmap for the number of logical paths that can exist in the diskarray device 11. The path group attribute information expresses, forexample, the validity or invalidity of a path group and a multipathgroup or a single-path group by means of a binary bitmap. Morespecifically, for example, the path group attribute informationexpresses path group invalidity/validity in bit position 0 (bit position0=0: path group is invalid; bit position 0=1: path group is valid), andexpresses a multipath group or single-path group in bit position 1 (bitposition 1=0: multipath group, bit position 1=1: single-path group). Inaddition, for example, the name of a connected host is expressed in thepath group attribute information by means of a predetermined method (abitmap, for example).

The channel control unit 4 references the LU control table of the targetvolume (table registered in the control memory 7), capturespredetermined items such as online host discrimination information (thehost name, for example), and registers the name of the host (or otherhost discrimination information), and so forth, as path groupinformation on the basis of the predetermined items thus captured. Theuser is able to identify whether there is a single host or a pluralityof hosts connected to the target volume, as well as the name of theconnected host(s), and so forth, by referencing the path groupinformation.

The online information control table 14 and the path group informationcontrol table 15 were described above.

Next, an outline of the first to fourth processing flows, which areexecuted when the AP2 issues the above copy command of the storagesystem pertaining to the present embodiment, will be provided.

First, an outline of the first processing flow will be provided withreference to FIG. 4.

A plurality of CU numbers, and an LU management table, in which two ormore LUN corresponding with each CU number are recorded, exist in apredetermined storage region of the host 1 (a certain directory on thehard disk, for example). For example, the two or more (256, for example)LUN corresponding with each CU number are consecutive (by way ofexample, the 256 LUN corresponding with a certain CU number are ‘0’ to‘255’, and the 256 LUN corresponding with the next CU number are ‘256’to ‘511’).

The AP of the host 1 (hereinafter called the ‘host AP’) 2 receivescopying requests. When a copying request is received, the host AP2receives an input of predetermined required parameters, such as the CUnumber of the copy source CU and one or more optional LUN in this CU,the CU number of the copy destination CU and one or more optional LUN inthis CU, as well as which LUN of the copy source is to be paired withwhich LUN of the copy destination. Further, when a single LUN is inputto the copy source and/or the copy destination, the host AP2 mayreference the LU management table and specify the CU number includingthe inputted LUN, or this CU number may be input automatically. The hostAP2 may also issue a predetermined report to the user if a LUN notincluded in the CU number is not input.

Further, once copying has been designated by the user when the aboverequired parameters have been input, the host AP2 performs the followingprocessing before generating a copy command (or recopy command)containing the required parameters thus input and issuing this commandto the disk array device 11.

The host AP2 generates an examination command 12 with target informationthat includes information with the CU number of the copy destination CU(subvolume group) inputted by the user and relaying the fact that thereis a plurality of subvolumes, and information indicating ‘within unit’as the control flag. The host AP2 then sends this examination command 12to the connection-destination disk array device 11 of the host 1.

Upon identifying from the received examination command 12 that thecontrol flag is ‘within unit’ and that a CU number is included in thetarget information, the channel control unit 4 of the disk array device11 accesses the control memory 7, specifies a plurality of LUNcorresponding with the CU number, and references the plurality of LUcontrol tables corresponding with the specified plurality of LUN. Then,the channel control unit 4 extracts a plurality of ON/OFF informationitems (0 or 1 one-bit information items) from the plurality of LUcontrol tables thus referenced, and generates an online informationcontrol table 14 corresponding with the target CU (that is, acopy-destination subvolume group), on the basis of the extractedplurality of ON/OFF information items, the CU number and plurality ofLUNs, and so forth. The channel control unit 4 then sends the generatedonline information control table 14 to the host 1.

When the number of online volumes recorded in the online informationcontrol table 14 thus received is one or more, the host AP2 referencesthe LU management table, and, by comparing one or more LUN inputted bythe user beforehand with the ON/OFF list recorded in the table 14, makesan ON/OFF judgment of whether the subvolume 10B with the LUN inputted bythe user is in the online state (the LUN corresponding with each bit canbe specified depending on what number from the start or end each bit isin the ON/OFF list).

If the result of this ON/OFF judgment is that all the subvolumes 10Bwith the LUN inputted by the user are in the offline state (or thenumber of online volumes recorded in the online information controltable 14 is zero), the host AP2 generates a copy command that containsthe required parameters inputted by the user and issues this copycommand to the disk array device 11.

On the other hand, if the result of this ON/OFF judgment is that thereis even one online LUN among the one or more LUN inputted by the user,the host AP2 displays this fact. Further, the host AP2 responds to acommand from the user (or immediately without consulting the user oncethe existence of an online LUN has been identified), an examinationcommand 12 for obtaining path group information is generated for eachsubvolume that is specified as being online. That is, the host AP2separately generates, for each subvolume specified as being online, anexamination command 12 that has information indicating ‘within unit’ asa control flag and target information relaying the fact that this is asingle volume and containing the LUN of this subvolume. The host AP2then sends each generated examination command 12 to theconnection-destination disk array device 11 of the host 1. Further,here, the designation of a single volume by the target information ofthe examination command 12 need not necessarily be generated based onthe information of the received online information control table 14. Thetarget information may simply contain the LUN desired by the user forwhich path group information is desired, for example.

When it is identified from the received examination command 12 that thecontrol flag is ‘within unit’ and the target information indicates asingle volume and contains the LUN of this volume, the channel controlunit 4 of the disk array device 11 accesses the control memory 7 toreference the LU control group corresponding with this LUN. Then, thechannel control unit 4 acquires the names of one or more connected hostsfrom the referenced LU control table, generates a path group informationcontrol table 15 with path group information that contains these one oremore connected-host names, and then sends this path group informationcontrol table 15 to the host 1.

Based on the received path group information control table 15, the hostAP2 displays path group information (information containing then namesof the hosts connected to the subvolume) for each online subvolume onthe user interface of the host 1.

According to this processing flow, before the copy source volume andcopy destination volume desired by the user are paired and data iscopied, an ON/OFF judgment of whether the subvolume designated by theuser is in an online state is performed. If the result of this ON/OFFjudgment is that the subvolumes designated by the user are all in anoffline state, copying is executed, and, if even one online subvolume ispresent among the designated subvolumes, copying is not executed and anexamination regarding the path group information for the onlinesubvolume is made and displayed on the host 1. By viewing this pathgroup information, the user is then able to specify easily whichseparate host(s) 1 is (are) connected to the subvolume. Stating thisusing the illustrated example, it can be seen from the onlineinformation control table 14 received by way of response to the firstexamination command 12, that one subvolume 10B is in an online state,and it is clear from the path group information control table 15received by way of response to the second examination command 12 that,of the hosts 1A to 1E separate from host 1, hosts 1B and 1D areconnected to the single subvolume 10B.

Further, in the above processing flow, when it is detected that even oneonline LUN is present among the copy destination LUNs inputted by theuser, the host AP2 may issue an examination command 12 for acquiringpath group information for each online subvolume automatically with orwithout consulting the user (this is the same as the third processingflow described subsequently).

FIG. 12 shows a sequence of commands between the host 1 and disk arraydevice 11 in the processing flow illustrated in FIG. 4. The content ofthe command sequence in FIG. 12 will be described below for therespective processing of S201 to S208.

S201:

The host 1 generates a second examination command 12 in order to obtainpath group information on the logical volume 10 contained in the CU(information containing names of hosts connected to the subvolume). Inthe second examination command 12 of this case, ‘within unit’ isdesignated as the control flag, and ‘single volume’ is designated as thetarget information (further, as it is generated here, in the case of thefirst examination command 12 for obtaining online information for thelogical volume 10 in the target CU, ‘within unit’ is designated in thiscommand 12 as the control flag, and ‘plurality of volumes’ is designatedas the target information.

S202:

The host 1 issues the generated second examination command 12 (or firstexamination command 12) to the disk array device 11.

S203:

The disk array device 11 reports the completion of the transfer of thesecond examination command 12 (or first examination command 12) to thehost 1.

S204:

The disk array device 11 generates the path group information controltable 15 (or online information control table 14).

S205:

The disk array device 11 issues a completion report to the effect thatthe generation of the path group information control table 15 (or onlineinformation control table 14) is complete, and a data-transferpreparations completion report to the host 1.

S206:

The host 1 issues a request to transfer the data of the path groupinformation control table 15 (or online information control table 14) tothe disk array device 11.

S207:

The disk array device 11 transfers the data of the generated path groupinformation control table 15 (or online information control table 14) tothe host 1.

S208:

The disk array device 11 issues a normal completion report for the datatransfer of the path group information control table 15 (or onlineinformation control table 14) and a completion report for the secondexamination command (or first examination command) 12 to the host 1.

As a result of this command sequence, the host 1 issues a command to thedisk array device 11 and receives the data requested.

Next, an outline of the second processing flow that is executed when theAP2 issues the above-mentioned copy command of the storage systempertaining to this embodiment will be provided with reference to FIG. 5.In the following description, parts that are different from those of thefirst processing flow are described; and the description of those partsthat are the same will be omitted or simplified (this is also true ofthe third and fourth processing flows below).

The host AP2 performs the following processing before issuing a copyinstruction for the logical volume 10 to the disk array device 11, forexample.

The host AP2 receives the online information control table 14 from thedisk array device 11 by means of the same method as the first processingflow and makes an ON/OFF judgment of whether the copy destination LUNinputted by the user is in the online state.

When the result of this ON/OFF judgment is that an online copydestination volume (subvolume) has been specified, the host AP2generates a setting cancellation command 13 that includes targetinformation with the LUN of the specified subvolume and relaying thefact that there is a single subvolume, and a clear instruction, that is,a setting cancellation command for canceling the path group informationof the subvolume 10B (stated differently, a setting cancellation commandfor compulsorily switching the subvolume 10B from the online state tothe offline state) 13, and sends this command to the disk array device11.

The disk array device 11 receives the setting cancellation command 13from the host AP2, cancels the path group information settings byaccessing the LU control table (table of the control memory 7)corresponding with the LUN in the command 13, and changes the ON/OFFinformation from a ‘0’ representing the online state to a ‘1’representing an offline state. Thereafter, the channel control unit 4sends a completion report regarding the cancellation of the path groupinformation to the host 1.

According to this processing flow, before the copy source volume andcopy destination volume desired by the user are paired and data copyingis executed, an ON/OFF judgment of whether the subvolume designated bythe user is in the online state is performed. If the result of thisON/OFF judgment is that even one subvolume among the subvolumesdesignated by the user is an online subvolume, copying is not executedand the online subvolume can be compulsorily converted to an offlinestate. Stated using the illustrated example, the connection between onesubvolume 10B and the separate hosts 1B and 1D is compulsorily broken.Thereafter, the channel control unit 4 sends the cancellation completionreport to the host 1, and, once the copy command (or recopy command) isreceived from the host AP2 by way of response, data may be immediatelycopied from the copy source CU to the copy destination CU. In this case,the content of the copied data may be the content when the copying isexecuted or may be content that is obtained by means of a snapshot atthe time the first examination command is received from the user.

Further, in the above processing flow, when it is detected that even oneonline LUN is present among the copy destination LUNs inputted by theuser, the host AP2 may issue a setting cancellation command 13 forcompulsorily converting the online subvolume to an offline stateautomatically with or without consulting the user. Further, afterdetecting an online subvolume, the host 1 or disk array device 11 mayinquire whether the connection with all (or a preset portion of) theseparate hosts connected to the online subvolume may be compulsorilybroken at a predetermined time (such as immediately following detectionor when the setting cancellation command 13 is received, for example).In this case, when an affirmative reply is obtained from all theseparate hosts, the host 1 or disk array device 11 compulsorily convertsthe subvolume to the offline state, and when an affirmative reply is notobtained, discrimination information for a separate host for which anaffirmative reply has not been obtained may be displayed on the displayscreen of the host 1 (at this stage, the description is the same as thatof the fourth processing flow described subsequently).

However, the disk array device 11 may possess a function for preventingpath cancellation by a connected host. For example, the user can alsowrite information in a predetermined storage medium of the controlmemory or the like of the disk array device 11 beforehand so that evenwhen a setting cancellation command 13 from another host (a pathcancellation command, for example) is received, this cancellation is notexecuted. Accordingly, even when path cancellation information has beensent by mistake, it is possible to prevent path cancellation (that is,the forced conversion of an online state into an offline state) for avolume for which the online state with the host is always retained.

FIG. 13 shows a sequence of commands between the host 1 and disk arraydevice 11 for the processing flow illustrated in FIG. 5. The content ofthe command sequence in FIG. 13 will be described below for therespective processing of S301 to S305.

S301:

In order to erase the path group information of the control memory 7,the host 1 generates a setting cancellation command 13. In the settingcancellation subcommand 13 of this case, ‘within unit’ is designated asthe control flag, and ‘single volume’ is designated as the targetinformation.

S302:

The host 1 issues the second subcommand 13 thus generated to the diskarray device 11.

S303:

The disk array device 11 reports the fact that the transfer of thesecond subcommand 13 is complete to the host 1.

S304:

The disk array device 11 erases the path group information recorded inthe LU control table of the logical volume 10 designated by the settingcancellation command 13.

S305:

The disk array device 11 then issues a normal completion report for thepath group information cancellation and a completion report for thesetting cancellation command 13 to the disk array device 11.

The path group information is erased by this command sequence.

Next, an outline of the third processing flow that is executed when theabove-mentioned copy command is issued by the AP2 of the storage systempertaining to this embodiment will be provided with reference to FIG. 6.

In the third processing flow (and the fourth processing flow describedsubsequently), one or more (one, for example) separate device 11A isconnected to the connection-destination disk array device 11 of the host1. A plurality of regular volumes 10A in one copy source CU is presentin the connection-destination disk array device 11 and a plurality ofsubvolumes 10B in the one copy destination CU is present in the separatedisk array device 11A. The control unit 100 of theconnection-destination disk array device 11 and the control unit 100A ofthe separate disk array device 11A comprise elements other than thephysical disk groups 9 shown in FIG. 1, for example.

Once copying is designated by the user by inputting the requiredparameters (the copy destination CU number and LUN, for example), thehost AP2 performs the following processing before a copy command (orrecopy command) containing the inputted required parameters is generatedand issued to the disk array device 11.

The host AP2 generates a first examination command 12 that has targetinformation with the CU number of the copy destination CU (subvolumegroup) that was input by the user and relaying the fact that there is aplurality of subvolumes, as well as information indicating a ‘separateunit’ as the control flag, and sends this first examination command 12to the connection-destination disk array device 11 of the host 1. Inthis case, when it is discriminated from the received examinationcommand 12 that the control flag is ‘separate unit’, the channel controlunit 4 that receives the examination command 12 transfers theexamination command 12 to the separate channel control unit (not shown)of the separate disk array device 11A (here, the channel control unit 4may take measures for changing the control flag from ‘separate unit’ to‘within unit’, to prevent an output from a separate channel controlunit).

When the separate channel control unit of the disk array device 11Areceives an examination command 12 from the channel control unit 4 andit is identified that a CU number is contained in the targetinformation, this separate channel control unit accesses control memory7A, specifies a plurality of LUN corresponding with this CU number, andreferences a plurality of LU control tables corresponding with theplurality of LUN thus specified. Then, the separate channel control unitextracts a plurality of ON/OFF information items (0 or 1 one-bitinformation) from the plurality of LU control tables thus referenced,and, based on the extracted plurality of ON/OFF information items andthe CU number and plurality of LUNs, generates an online informationcontrol table 14 that corresponds with the target CU (that is, a copydestination subvolume group). The separate channel control unit thensends the online information control table 14 thus generated to the diskarray device 11. The disk array device 11 transfers the onlineinformation control table 14 to the host 1.

The second examination command 12 (that is, in which the control flag is‘separate unit’) is sent from the host AP2 to the separate disk arraydevice 11A via the disk array device 11, and, by way of response to thissecond examination command 12, the path group information control table15 is generated and then sent via the disk array device 11 to the host 1before being displayed thereby. However, the second examination command12 need not necessarily pass via the disk array device 11. Instead, theonline information control table 14 can be reported to the host system1. For example, the information in the online information control table14 may be sent between host systems.

According to this processing flow, stating this by means of theillustrated example, as a result of the processing in response to thefirst examination command 12, it is clear that one subvolume 10B in theseparate disk array device 11A is in the online state, and, as a resultof the processing in response to the second examination command 12, itis clear that the separate host 1E is connected to the subvolume 10B.

FIG. 14 shows a sequence of commands between the host 1, disk arraydevice 11, and a separate disk array device 11A for the processing flowillustrated in FIG. 6. The content of the command sequence in FIG. 14will be described below for the respective processing of S401 to S413.

S401:

The host 1 generates a second examination command 12 in order to obtainpath group information on the logical volumes 10 contained in the CU(information including the names of the hosts connecting to thesubvolume). In the second examination command 12 of this case, ‘separateunit’ is designated as the control flag and ‘single volume’ isdesignated as the target information (as it is generated here, in thecase of the first examination command 12 for obtaining onlineinformation for the logical volume 10 in the target CU, ‘separate unit’is designated as the control flag, and ‘plurality of volumes’ isdesignated as the target information in command 12.

S402:

The host 1 issues the generated second examination command 12 (or firstexamination command 12) to the disk array device 11.

S403:

The disk array device 11 that receives the second examination command 12from the host 1 reforms the second examination command (or firstexamination command) 12 as the second examination command (or firstexamination command) 12A in order to make it possible to issue thesecond examination command (or first examination command) 12 to theseparate disk array device 11A (or another disk array device). In thiscase, if the second examination command (or first examination command)12 itself is in the form of a command that can be issued to the separatedisk array device 11A (or another disk array device), the command neednot be reformed. The disk array device 11 issues the second examinationcommand (or first examination command) 12A to the disk array device 11A.

S404:

The disk array device 11 reports the completion of the transfer of thesecond examination command (or first examination command) 12 to the host1.

S405:

The separate disk array device 11A that receives the second examinationcommand (or first examination command) 12A then generates a path groupinformation control table 15 (or online information control table 14).

S406:

After generating the path group information control table 15 (or onlineinformation control table 14), the separate disk array device 1A issuesa normal completion report to the effect that the path group informationcontrol table 15 (or online information control table 14) has beengenerated and a data-transfer preparations completion report to the diskarray device 11.

S407:

The disk array device 11 issues a request to transfer the data of thepath group information control table 15 (or online information controltable 14) to the separate disk array device 11A.

S408:

The separate disk array device 11A then issues the data of the generatedpath group information control table 15 (or online information controltable 14) to the disk array device 11.

S409:

The separate disk array device 11A issues a normal completion report forthe data transfer of the path group information control table 15 (oronline information control table 14) and a completion report for thesecond examination command (or first examination command) 12A to thedisk array device 11.

S410:

The disk array device 11 issues a completion report regarding thecompletion of the generation of the path group information control table15 (or online information control table 14) and a data-transferpreparations completion report to the host 1.

S411:

The host 1 issues a request to transfer the data of the path groupinformation control table 15 (or online information control table 14) tothe disk array device 11.

S412:

The disk array device 11 then transfers the data of the path groupinformation control table 15 (or online information control table 14)received from the disk array device 11A to the host 1.

S413:

The disk array device 11 issues a normal completion report for the datatransfer of the path group information control table 15 (or onlineinformation control table 14) and a completion report for the secondexamination command (or first examination command) 12 to the host 1.

As a result of this command sequence, the host 1 issues a command to thedisk array device 11A via the disk array device 11 and receives the datarequested.

Next, an outline of the fourth processing flow that is executed when theAP2 issues the above-mentioned copy command of the storage systemaccording to this embodiment will be provided with reference to FIG. 7.In the following description, parts that are different from those of thethird processing flow are described, while the description of thoseparts that are the same will be omitted or simplified.

In the fourth processing flow, similarly to the third processing flow,the host AP2 receives the online information control table 14 from theseparate disk array device 11A via the connection-destination disk arraydevice 11, and performs an ON/OFF judgment of whether the copydestination LUN inputted by the user is in the online state.

When the result of the ON/OFF judgment is that an online copydestination volume (subvolume) has been specified, the host AP2generates a setting cancellation command 13 that includes a control flagindicating ‘separate unit’, target information with the LUN of thespecified subvolume and relaying the fact that there is a single volume,and a clear instruction, and then sends this setting cancellationcommand 13 to the disk array device 11.

The separate channel control unit of the separate disk array device 11Athat receives the setting cancellation command 13 from the disk arraydevice 11 accesses the LU control table (table in the control memory 7A)corresponding with the LUN in the command 13 to cancel the path groupinformation settings, and then changes the ON/OFF information from a ‘0’expressing the online state to a ‘1’ expressing the offline state.Thereafter, the separate channel control unit sends a completion reportthat the path group information has been cancelled to the host 1 via thedisk array device 11. However, the disk array device 11A may have afunction preventing path cancellation by a host that is not directlyconnected. For example, the user or similar is also able to writeinformation in the control memory or the like of the disk array device11A beforehand so that, even when a path cancellation command isreceived from another host, this path cancellation is not executed.Accordingly, even when path cancellation information has been sent fromanother host system in error, path cancellation can be prevented forthose volumes whose online state with the host is to be continuallypreserved.

FIG. 15 shows a sequence of commands between the host 1, disk arraydevice 11, and a separate disk array device 11A for the processing flowillustrated in FIG. 7. The content of the command sequence in FIG. 15will be described below for the respective processing of S501 to S507.

S501:

The host 1 generates a setting cancellation command 13 in order to erasepath group information of the control memory 7. In the settingcancellation command 13 of this case, ‘separate unit’ is designated asthe control flag and ‘single volume’ is designated as the targetinformation.

S502:

The host 1 issues the setting cancellation command 13 thus generated tothe disk array device 11.

S503:

The disk array device 11 that receives the setting cancellation command13 from the host 1 reforms the setting cancellation command 13 as thesetting cancellation command 13A in order to make it possible to issuethe setting cancellation command 13 to the disk array device 11A oranother disk array device. In this case, if the setting cancellationcommand 13 itself is in the form of a command that can be issued to thedisk array device 11A or another disk array device, there is no need toreform the command. The disk array device 11 issues the settingcancellation command 13A to the disk array device 11A.

S504:

The disk array device 11 reports the completion of the transfer of thesetting cancellation command 13 to the host 1.

S505:

The disk array device 11A that receives the setting cancellation command13A erases path group information of the target in the control memory 7in the disk array device 11A (that is, path group information in an LUmanagement table corresponding with the logical volume that isdesignated in this command 13A).

S506:

After erasing path group information of the control memory 7, the diskarray device 11A issues a normal completion report for the path groupinformation erasure and a completion report for the setting cancellationcommand 13A to the disk array device 11.

S507:

The disk array device 11 issues a normal completion report for the pathgroup information erasure and a completion report for the settingcancellation command 13 to the disk array device 11.

S508:

As a result of this command sequence, the host 1 issues a settingcancellation command to the disk array device 11A via the disk arraydevice 11 to erase path group information for the logical volumerequested.

The processing flow that is executed by the above storage system will bedescribed below with reference to the flowcharts of FIGS. 8 to 10.

FIG. 8 is a flowchart of the processing that is executed when the firstexamination command for receiving the provision of the onlineinformation control table 14 is issued.

When an input of the required parameters that are designated for copyingis received and copying is designated, the host AP2 judges (step S18)whether the copy destination CU exists within the unit (within theconnection-destination disk array device 11) or in a separate unit(outside the connection-destination disk array device 11) on the basisof the required parameters and the LU management table (a table thatcontains information on which disk array device each CU is in, forexample) (or stated differently, the host AP2 judges the copying type).

When the result of S18 is that the copying type is copying within theunit, the host AP2 specifies the copy destination CU number from theparameters inputted in order to perform the copying, generates a firstexamination command 12 that includes target information with the copydestination CU number and a control flag signifying ‘within unit’, andissues the first examination command to the disk array device 11 (S19).

The channel control unit 4 of the disk array device 11 reports that thefirst examination command 12 has been received to the host 1, generatesthe online information control table 14 by means of the above method onthe basis of the information in the first examination command 12, andthen sends a generation completion report to the host 1 (S20). In theonline information control table 14, for example, the ‘number of onlinevolumes’ denotes the number of logical volumes that are online among 256logical volumes 10 contained in the target CU and is therefore expressedby a value from X′ 0000′to X′ 0100′. Further, for example, ‘examinationtarget information’ denotes information that is the SSID and CU numberthat the target logical volume 10 comprises and the product number ofthe disk array device 11. Further, for example, the ‘ON/OFF list’ has256 one-bit information items (‘0’ indicating an online state or ‘1’indicating an offline state) corresponding with 256 logical volumes 10included in the target CU.

The channel control unit 4 receives an instruction to acquire the onlineinformation control table 14 from the host 1 in response to thegenerated completion report, and, in response to this acquisitioninstruction, reports the generated online information control table 14to the host 1 (S21). Thereafter, the channel control unit 4 communicatesthe normal status to the host 1 (S29) and the processing ends (S30).

Furthermore, when the result of S18 is that the copying type is copyingto a separate unit (copying takes place between theconnection-destination disk array device 11 and the separate disk arraydevice 11A), the host AP2 generates the first examination command 12that includes a control flag denoting a ‘separate unit’ and issues thefirst examination command 12 to the disk array device 11 (S22).

Next, the channel control unit 4 of the disk array device 11 thatreceives the first examination command 12 issues the first examinationcommand 12 thus received to the separate disk array device 11A. Thechannel control unit 4 communicates the fact that the transfer of thefirst examination command 12 to the separate disk array device 11A iscomplete to the host 1 and hence the channel control unit 4 makes aswitching request to the host 1 (more specifically, for example, arequest to disconnect a predetermined communication among a plurality ofcommunications) (S23) Accordingly, the host 1 switches the connectionbetween the host 1 and the disk array device 11.

Next, the separate channel control unit of the separate disk arraydevice 11A that receives the first examination command 12 generates theonline information control table 14 based on information in this command12 and sends a generation completion report to the disk array device 11(S24).

In response to this generation completion report, the disk array device11 issues an instruction to acquire the online information control table14 to the separate disk array device 11A. In response to thisacquisition instruction, the separate disk array device 11A then reportsthe generated online information control table 14 to theconnection-destination disk array device (S25). The separate disk arraydevice 11A then communicates the normal status to theconnection-destination disk array device 11 (S26).

By way of response to the communication regarding the normal status, theconnection-destination disk array device 11 reports the completion ofthe command processing to the host 1. The connection-destination diskarray device 11 takes advantage of the fact that the completion of thecommand processing has been reported to the host 1 to communicate arequest for reconnection to the host 1 (S27).

In response to this reconnection request, the host 1 issues aninstruction to acquire the online information control table 14 to theconnection-destination disk array device 11. In response to theacquisition instruction, the connection-destination disk array device 11communicates the online information control table 14 that has beentransferred by the separate disk array device 11A to the host 1 (S28).Thereafter, the connection-destination disk array device 11 communicatesthe normal status to the host 1 (S29) and the processing ends (S30).

FIG. 9 is a flowchart for the processing that is executed when a secondexamination command for receiving the provision of a path groupinformation control table 15 is issued.

The host AP2 executes the following processing when, for example, as aresult of a comparison of the reported online information control table14 and the inputted required parameters, it is identified that there iseven one online subvolume among a plurality of subvolume LUNs inputtedby the user.

The host AP2 judges (S31) whether the copy destination CU exists withinthe unit (within the connection-destination disk array device 11) or ina separate unit (outside the connection-destination disk array device11) based on the required parameters inputted by the user and the LUmanagement table (a table that contains information on which disk arraydevice each CU is in, for example) (or stated differently, the host AP2judges the copying type).

When the result of S31 is that the copying type is copying within theunit, the host AP2 generates a second examination command 12 thatincludes target information with the LUN of an online and specifiedsubvolume (LUN inputted by the user), and a control flag signifying‘within unit’, and then issues this second examination command 12 to thedisk array device 11 (S32).

The channel control unit 4 of the disk array device 11 reports thereceipt of the second examination command 12 to the host 1, generatesthe path group information control table 15 by means of the above methodon the basis of the LU control table corresponding with the LUN in thesecond examination command 12, and then sends a generation completionreport to the host 1 (S33). In the path group information control table15, for example, where ‘the number of online paths’ is concerned, thenumber of paths established for the logical volume 10 constituting thetarget is indicated by a value in base 16 from X′ 000′ to X′ 100′.Further, for example, ‘examination target information’ includesinformation that is the address of the target logical volume 10, theSSID and CU number that the logical volume 10 comprises, and the productnumber of the disk array device 11 (in the ‘separate unit’ case, theseparate disk array device 11A). In addition, for example, ‘path groupinformation’ denotes the number of a logical path set in the targetvolume, and path group attribute information. The logical path number isthe number of an online logical paths. More specifically, for example,whether the logical path is online or not is expressed by the binarydigits 1 and 0 (0: online, an 1: offline), and these bits are expressedin the format of a bitmap for the number of logical paths that can existin the disk array device 11. The path group attribute informationexpresses, for example, the validity or invalidity of a path group and amultipath group or a single-path group by means of a binary bitmap.

The channel control unit 4 receives an instruction to acquire the pathgroup information control table 15 from the host 1 in response to theabove-mentioned generation completion report, and, in response to thisacquisition instruction, reports the generated path group informationcontrol table 15 to the host 1 (S34). Thereafter, the channel controlunit 4 communicates the normal status to the host 1 (S42) and theprocessing ends (S43).

Further, when the result of S31 above is that the copying type iscopying to a separate unit, the host AP2 generates a second examinationcommand 12 that includes a control flag signifying ‘separate unit’ andissues this second examination command 12 to the disk array device 11(S35).

Next, the channel control unit 4 of the disk array device 11 thatreceives the second examination command 12 issues the received secondexamination command 12 to the separate disk array device 11A. Thechannel control unit 4 communicates the fact that the second examinationcommand 12 has been transferred to the separate disk array device 11A tothe host 1 and hence the channel control unit 4 issues a switchingrequest to the host 1 (more specifically, for example, a request todisconnect a predetermined communication among a plurality ofcommunications (S36). Accordingly, the host 1 switches the connectionbetween the host 1 and the disk array device 11.

Next, the separate channel control unit of the separate disk arraydevice 11A that receives the second examination command 12 generates thepath group information control table 15 on the basis of information inthis command 12 and sends a generation completion report to the diskarray device 11 (S37).

In response to the generation completion report, the disk array device11 issues an instruction to acquire the path group information controltable 15 to the separate disk array device 11A, and, in response to thisacquisition instruction, the separate disk array device 11A reports thegenerated path group information control table 15 to theconnection-destination disk array device 11 (S38). Further, the separatedisk array device 11A communicates the normal status to theconnection-destination disk array device 11 (S39).

In response to the communication regarding the normal status, theconnection-destination disk array device 11 reports the completion ofthe command processing to the host 1. The connection-destination diskarray device 11 takes advantage of the fact that the completion of thecommand processing has been reported to the host 1 to communicate arequest for reconnection to the host 1 (S40).

In response to this reconnection request, the host 1 issues aninstruction to acquire the path group information control table 15 tothe connection-destination disk array device 11. By way of response tothis acquisition instruction, the connection-destination disk arraydevice 11 reports the path group information control table 15 that hasbeen transferred by the separate disk array device 11A to the host 1(S41). Thereafter, the connection-destination disk array device 11communicates the normal status to the host 1 (S42) and the processingends (S43).

FIG. 10 is a flowchart for the processing that is executed when asetting cancellation command 13 for changing the subvolume from anonline state to an offline state is issued.

The host AP2 judges (step S44) whether the copy destination CU existswithin the unit (within the connection-destination disk array device 11)or in a separate unit (outside the connection-destination disk arraydevice 11) on the basis of the required parameters inputted by the userand the LU management table (a table that contains information on whichdisk array device each CU is in, for example) (stated differently, thehost AP2 judges the copying type).

When the result of S44 is that the copying type is within the unit, thehost AP2 generates a setting cancellation command (a command in whichthe control flag is ‘within unit’) 13 that includes the LUN of theonline subvolume among the required parameters inputted by the user, andsends this setting cancellation command 13 to the disk array device 11(S45).

The channel control unit 4 of the disk array device 11 accesses the LUcontrol table corresponding with the LUN included in the receivedsetting cancellation command 13 to cancel path group informationrecorded in the LU control table, and changes the ON/OFF informationfrom an online state ‘0’ to an offline state ‘1’ (S46). Thereafter, thechannel control unit 4 communicates the normal status to the host 1(S52) and the processing ends (S53).

Meanwhile, when the result of S44 is that the copying type is copyingbetween separate units, the host AP2 generates a setting cancellationcommand (a command in which the control flag is ‘separate unit’) 13 thatincludes the LUN of the online subvolume among the required parametersinputted by the user, and sends this setting cancellation command 13 tothe disk array device 11 (S47).

The disk array device 11 transfers the setting cancellation command 13received from the host 1 to the separate disk array device 11A.Thereafter, the disk array device 11 communicates the fact that thetransfer to the separate disk array device 11A has been completed to thehost 1, and hence the disk array device 11 issues a switching request tothe host 1 (more specifically, for example, a request to disconnect apredetermined communication among a plurality of communications (S48).Accordingly, the host 1 switches the connection between the host 1 andthe disk array device 11.

In response to the setting cancellation command 13 that has beentransferred, the separate disk array device 11A references the LUcontrol table corresponding with the LUN in the setting cancellationcommand 13 to cancel the path group information from the LU controltable (S49) Thereafter, the separate disk array device 11A communicatesthe normal status to the disk array device 11 (S50).

The disk array device 11 that has received notice of the normal statusreports the completion of the command processing to the host 1.Thereafter, the disk array device 11 takes advantage of the fact thatthe completion of the command processing has been reported to the host 1to communicate a reconnection request to the host 1 (S51). Then the diskarray device 11 communicates the normal status to the host 1 (S52) andthe processing accordingly ends (S53).

According to the embodiment above, the path group information regardingwhich host each volume is connected to is registered in the controlmemory 7 for each of the logical volumes 10. Before a copy command isissued by the host 1 and data copying is performed, it is judged whetherthe target subvolume is in an online state, and if same is indeed in theonline state, path group information corresponding with the targetsubvolume is sent to and displayed by the host 1. Accordingly, the userof the host 1 is able to specify easily to which separate host thetarget subvolume is connected and hence the load for converting thesubvolume to the offline state is reduced.

Further, according to the above embodiment, before data copying isperformed, the first and second examinations are performed, and, whenthe target subvolume is switched from the online state to the offlinestate after the second examination, data copying is executed.Accordingly, data is backed up normally to the database formed by theplurality of subvolumes.

Further, according to the above embodiment, if the host AP2 sends thesetting cancellation command 13 to the disk array device 11, the targetsubvolume is switched from the online state to the offline state.Therefore, a subvolume that is in an online state can be convertedeasily to the offline state.

Further, several modified examples as detailed below may be consideredin the above embodiment.

For example, in a first modified example, the channel control unit 4,which generates the online information control table 14, may record notonly ‘1’ or ‘0’ one-bit information in the ON/OFF list, but also thenumber (LUN) of each logical volume corresponding with each one-bitinformation item.

In a second modified example, upon receiving a first examination commandin addition to the input of the CU number of the target CU or the LUN ofthe target volume from the user, the host AP2 may generate a firstexamination command 12 and send same to the disk array device 11.Similarly, upon receiving a second examination command in addition tothe input of the LUN of the target volume from the user, the host AP2may generate a second examination command 12 and send same to the diskarray device 11.

In a third modified example, ON/OFF information need not be present inthe LU control table corresponding with the LU. In this case, an onlinestate or offline state may be judged according to the presence orabsence of path group information.

In a fourth modified example, the host AP2 may generate and send a copycommand (or recopy command) to the disk array device 11 instead ofissuing a first examination command or second examination command, orthe like. In this case, the channel control unit 4 of the disk arraydevice 11 executes a first examination at the time the copy command (orrecopy command) is received (and executes a second examination if needbe). As a result of the first examination (and of the secondexamination), as long as there is no obstacle to copying, copying isexecuted, and if such an obstacle exists, the examination result may bereported to the user. Further, in this fourth modified example, thechannel control unit 4 converts all of the one or more target subvolumesin the online state to the offline state and may then execute copyprocessing according to the copy command (recopy command) received withpredetermined timing (immediately, for example).

An example of the operational flow of the disk array device 11 of thefourth modified example will be described below with reference to FIG.8.

The channel control unit 4 of the disk array device 11 receives the copycommand (or the recopy command) from the host 1 (S11). Before executingthis copy command (or recopy command), the channel control unit 4references one or more LU control tables corresponding with the one ormore copy destination LUN (that is, the LUN of one or more targetsubvolumes) included in this copy command, and then judges whether eachof the one or more target subvolumes is in the online state (S12).

When, as a result of S12, the channel control unit 4 judges that all ofthe one or more target subvolumes are in the offline state (NO in S12),the channel control unit 4 starts processing to execute the copyprocessing in accordance with the received copy command (or recopycommand) (S17). For example, when the disk array device 11 executes copyprocessing according to the copy command, all the data in the targetregular volumes is copied to the target subvolumes. Further, forexample, when the disk array device 11 executes copy processing inaccordance with a recopy command, only the updated data in the targetregular volumes is copied to the target subvolumes.

Meanwhile, when, as a result of the S12, the channel control unit 4judges that even one of the one or more target subvolumes is in theonline state (YES in S12), the channel control unit 4 judges whetheronline cancellation of the subvolume has been designated (S14). Thisjudgment can be performed on the basis of whether online cancellationdesignation information corresponding with the LUN of the targetsubvolume is included in the copy command (or recopy command) from thehost 1, or based on whether the LUN of the logical volume that mayundergo the online forced cancellation is registered in a predeterminedstorage medium of the control memory 7 or the like, for example.

When, as a result of S14, online cancellation has been designated forthe online target subvolume (YES in S14), the channel control unit 4changes the subvolume from an online state to an offline state (S16).Thereafter, the channel control unit 4 executes the processing of S17above.

On the other hand, when, as a result of S14, online cancellation has notbeen designated for the online target subvolume (NO in S14), the channelcontrol unit 4 generates the path group information control table 15 byacquiring path group information for the online subvolume from thecontrol memory, and reports this table 15 to the host 1 (S15). The host1 displays path group information that is written in the table 15, and,upon receiving the designation of the LUN of the target subvolume and asetting cancellation command from the user, generates a settingcancellation command 13 that includes this LUN before sending thissetting cancellation command 13 to the disk array device 11. The channelcontrol unit 4 then changes the online subvolume to the offline state inresponse to the setting cancellation command 13.

Further, in this operational flow, the procedure of the respectiveprocessing of S11 to S17 may be collectively defined and executed. Morespecifically, as pre-processing for copying, the processing of S11 toS17 may be performed.

According to the fourth modified example, when an online forcedcancellation is designated, the state of the subvolume is identifiedbeforehand. If this subvolume is in the online state, copy processing isexecuted after this state has been cancelled. Therefore, even when thesubvolume is in the online state, copying is performed after changingthis state to the offline state.

Further, in a fifth modified embodiment, at least one of the firstexamination and the second examination above may be executed by acomponent other than the channel control unit 4 in the disk array device11.

In the sixth modified example, even when a recopy command for copying issent once the paired state of each regular volume in the copy source CUand each subvolume in the copy destination CU has been cancelled and thepaired state then reformed, the host AP2 may send the first examinationcommand, second examination command, or the like, to the disk arraydevice 11. Further, as mentioned above, upon receiving a recopy command,the disk array device 11 may execute the first examination, secondexamination, or the like before executing copy processing in accordancewith this command.

In a seventh modified embodiment, a first examination command 12 orsecond examination command 12 may be included in a copy command orrecopy command. Further, a setting cancellation command 13 may beincluded in the copy command or recopy command. In this case, uponreceiving the copy command or recopy command, the channel control unit 4may execute the first examination command 12, second examination command12 and/or setting cancellation command 13 contained in this commandbefore executing the copy processing on the basis of this command.

Although embodiments and modified examples of the present invention havebeen described hereinabove, same are illustrations serving to explainthe present invention and are not intended to limit the scope of thepresent invention to these embodiments and modified examples alone. Thepresent invention can also be implemented in a variety of other forms.

For example, as a first aspect of the storage system according to thepresent invention, a plurality of volume groups containing two or morelogical volumes exists in the plurality of logical volumes. In thiscase, volume-group discrimination information for each of the pluralityof volume groups and two or more volume discrimination information itemscorresponding with two or more logical volumes contained in these volumegroups are recorded in the control memory. The storage control subsystemperforms a first examination of whether the two or more subvolumes arein an online state based on two or more ON/OFF information itemscorresponding with two or more subvolumes in a target subvolume groupcontaining the target subvolume (that is, performs a first examinationin volume-group units). When it is clear as a result of the firstexamination that the target subvolume among the two or more subvolumesis in an online state, the storage control subsystem performs the secondexamination with respect to the target subvolume and sends the result ofthe second examination to the certain host device.

For example, as a second aspect of the storage system according to thepresent invention, the certain host device of the first aspect generatesa first examination command that includes volume-group discriminationinformation on the target subvolume group and sends this firstexamination command to the storage control subsystem. In response to thefirst examination command received from the certain host device, thestorage control subsystem performs the first examination and sends thefirst examination result to the certain host device. The certain hostdevice then generates a second examination command that includesvolume-discrimination information on the target subvolume which isjudged from the first examination result as being in an online state andthen sends this second examination command to the storage controlsubsystem. By way of response to the second examination command receivedfrom the certain host device, the storage control subsystem performs asecond examination and sends the second examination result to thecertain host device. The certain host device then displays the secondexamination result.

For example, as a third aspect of the storage system according to thepresent invention, the ON/OFF information of the first aspect is one-bitinformation expressed by 1 or 0, and two or more one-bit informationitems corresponding with two or more subvolumes included in the targetsubvolume are included in the first examination result. The certain hostdevice stores, for each of the plurality of volume groups, avolume-group discrimination number, and a volume management table inwhich two or more volume discrimination numbers corresponding with twoor more logical volumes contained in the volume group are recorded inthis number order. Upon receiving an input of a volume discriminationnumber for the one or more target subvolumes from the user, the certainhost device generates the first examination command that includes thevolume discrimination number of the target subvolume group containingthe target subvolume and sends this first examination command to thestorage control subsystem, and, upon receiving the first examinationresult in response to this first examination command, judges whether theone or more target subvolumes is online on the basis of the two or moreone-bit information items included in the first examination result, theone or more volume discrimination numbers inputted by the user, and thevolume management table; and, upon judging that at least one targetsubvolume is in the online state, the certain host device generates thesecond examination command for the target subvolume and then sends thesecond examination command to the storage control subsystem.

For example, as a fourth aspect of the storage system according to thepresent invention, when the certain host device issues a copy commandafter volume discrimination information for the target regular volumeand volume discrimination information on the target subvolume have beeninput by the user and/or issues a recopy command for copying once thepaired state of the target regular volume and target subvolume has beencancelled and the paired state then reformed: an examination commandthat includes volume discrimination information on the target subvolumeis generated and sent to the storage control subsystem; and the firstand second examinations are performed before the target regular volumeand the target subvolume are paired and data in the target regularvolume is copied to the target subvolume.

For example, as a fifth aspect of the storage system according to thepresent invention, the certain host device receives a copy instructionfrom the user and issues a copy command in response to this copyinstruction after volume discrimination information for the targetregular volume and volume discrimination information on the targetsubvolume have been inputted by the user and/or issues a recopy commandfor copying once the paired state of the target regular volume andtarget subvolume has been cancelled and the paired state then reformed.When the storage control subsystem receives the copy command or recopycommand, before executing copy processing on the basis of this command,the storage control subsystem performs the first examination byreferencing ON/OFF information corresponding with discriminationinformation on the target subvolume that is included in this command,executing copy processing on the basis of the copy command or recopycommand upon judging that the target subvolume is in the offline stateas a result of the first examination but, on the other hand, executingthe second examination upon judging that the target subvolume is in theonline state as a result of this first examination.

For example, as a sixth aspect of the storage system according to thepresent invention, instead of or in addition to performing the secondexamination, the storage control subsystem switches the target subvolumefrom the online state to the offline state (for example, breaks theconnection between the target subvolume and the separate host device)when it is judged that the target subvolume is in the online state as aresult of the first examination.

For example, as a seventh aspect of the storage system according to thepresent invention, the storage control subsystem in the sixth aspectswitches the target subvolume from the online state to the offline state(changes the status indicated by the ON/OFF information of the targetsubvolume from online to offline, for example) in at least one of cases(1) to (3) below: (1) when a setting cancellation command that includesdiscrimination information on the target subvolume is received from thecertain host device after the second examination result is sent to thecertain host device; (2) when path group information corresponding withthe target subvolume is referenced, an inquiry is made with regard towhether the connection thereof with all or part of one or more separatehost devices specified based on this path group information may becancelled, and a reply relaying that the connection may be cancelled isthen obtained in response to this inquiry; and (3) when a predeterminedtime has elapsed after judging that the target subvolume is in an onlinestate (immediately after this judgment, for example).

For example, as an eighth aspect of the storage system according to thepresent invention, when a separate storage control subsystem isconnected to the storage control subsystem, the target regular volumeexists in the storage control subsystem, and the target subvolume existsin the separate storage control subsystem: the separate storage controlsubsystem references the control memory in the system, performs thefirst and second examinations, and sends the results of the first andsecond examinations to the certain host device. Each examination resultmay be sent to the certain host device via the storage control subsystemor directly without passing via the storage control subsystem.

Furthermore, for example, the disk array device 11 of the aboveembodiment can be implemented abstractly as detailed below.

The storage control subsystem comprises a plurality of logical volumesprepared on one or more physical storage devices; volume informationstorage means for storing, for each of the plurality of logical volumes,volume discrimination information, ON/OFF information expressing whetheror not each volume is in an online state, and path group informationwith regard to which host device a subvolume is connected to if in theonline state; first examination means for performing, as a result ofreceiving a specific command from a certain host device, a firstexamination of whether a target subvolume is in an online state based onthe ON/OFF information on the target subvolume before a target regularvolume and the target subvolume among the plurality of volumes arepaired and data in the target regular volume is copied to the targetsubvolume; second examination means for performing a second examinationwith regard to which separate host device the target subvolume isconnected to based on path group information on the target subvolumewhen, as a result of the first examination, it is clear that the targetsubvolume is in the online state; and second examination resultreporting means for sending the result of the second examination to thecertain host device.

1. A storage control subsystem that can communicably connect to a host,comprising: a disk portion that stores data sent by the host; a channelcontrol unit that constitutes an interface with the host; a disk controlunit that is connected to the disk portion and constitutes an interfacewith the disk portion; a cache memory unit that temporarily stores datathat is sent and received to and from the channel control unit and thedisk control unit; and a control memory that stores information on theconstitution of a plurality of logical volumes formed according to diskallocation, wherein the control memory comprises: online informationindicating whether a logical volume in the disk portion is online, andinformation on a path between the online logical volume and the host towhich the online logical volume is connected, wherein the storagecontrol subsystem receives a referral request for the online informationand the information of the path from the host via another storagecontrol subsystem, and, wherein when information on path cancellationwith respect to the online logical volume is received from the host viathe another storage control subsystem, the path cancellation withrespect to the online logical volume that is designated by the pathcancellation is executed.
 2. The storage control subsystem according toclaim 1, wherein, when the path cancellation information is receivedfrom a host connected via the another storage control subsystem, thedisk control unit functions so that the path cancellation is executed.3. A storage control subsystem connected to one or more host devices,comprising: a channel control unit that controls communications with theconnected one or more host devices; a plurality of logical volumesformed on one or more physical storage devices; a disk control unit thatcontrols the plurality of logical volumes; and a control memory inwhich, for each of the plurality of logical volumes, volumediscrimination information, ON/OFF information indicating whether anonline state exists, and, in the event of an online state, path groupinformation with regard to which host device a subvolume is connectedto, are recorded, wherein as a result of receiving a specific commandfrom a certain host device, the channel control unit performs, before atarget regular volume and target subvolume among the plurality ofvolumes are paired and data in the target regular volume is copied tothe target subvolume, a first examination of whether the targetsubvolume is in an online state based on the ON/OFF information on thetarget subvolume, and, when, as a result of this first examination, thetarget subvolume is known to be in an online state, the channel controlunit performs a second examination with regard to which separate hostdevice the target subvolume is connected to based on path groupinformation on the target subvolume, and wherein the result of thesecond examination is sent from the channel control unit to the certainhost device.
 4. The storage control subsystem according to claim 3,wherein a plurality of volume groups containing two or more logicalvolumes exist in the plurality of logical volumes, wherein volume-groupdiscrimination information for each of the plurality of volume groupsand two or more volume discrimination information items correspondingwith two or more logical volumes contained in these volume groups arerecorded in the control memory, wherein the storage control subsystemperforms a first examination of whether the two or more subvolumes arein an online state based on two or more ON/OFF information itemscorresponding with two or more subvolumes in a target subvolume groupcontaining the target subvolume, and wherein when it is clear as aresult of the first examination that the target subvolume among the twoor more subvolumes is in an online state, the storage control subsystemperforms the second examination with respect to the target subvolume andsends the result of the second examination to the certain host device.5. The storage control subsystem according to claim 4, wherein a firstexamination command that includes volume-group discriminationinformation on the target subvolume group is received from the certainhost device, and, in response to the first examination command, thefirst examination is performed and the result of the first examinationis sent to the certain host device, and wherein a second examinationcommand, which includes volume discrimination information on the targetsubvolume that has been judged as being in an online state based on thefirst examination result, is received from the certain host device, and,in response to the second examination command, the second examination isperformed and the result of the second examination is sent to thecertain host device.
 6. The storage control subsystem according to claim4, wherein the ON/OFF information is one-bit information expressed by 1or 0, wherein two or more one-bit information items corresponding withtwo or more subvolumes included in the target subvolume are included inthe first examination result, wherein the certain host device stores,for each of the plurality of volume groups, a volume-groupdiscrimination number, and a volume management table in which two ormore volume discrimination numbers corresponding with two or morelogical volumes contained in the volume group are recorded in thisnumber order, and wherein when an input of a volume discriminationnumber for the one or more target subvolumes is received from the user,the first examination command that includes the volume discriminationnumber of the target subvolume group containing the target subvolume isgenerated and sent to the storage control subsystem, and, when the firstexamination result is received in response to this first examinationcommand, it is judged whether the one or more target subvolumes isonline on the basis of the two or more one-bit information itemsincluded in the first examination result, the one or more volumediscrimination numbers inputted by the user, and the volume managementtable; and, when it is judged that at least one target subvolume is inthe online state, the second examination command is generated for thetarget subvolume and then sent to the storage control subsystem.
 7. Thestorage control subsystem according to claim 3, wherein, when thecertain host device issues a copy command after volume discriminationinformation for the target regular volume and volume discriminationinformation on the target subvolume have been input by the user and/orissues a recopy command for copying once the paired state of the targetregular volume and target subvolume has been cancelled and the pairedstate then reformed, wherein an examination command that includes volumediscrimination information on the target subvolume is generated and sentto the storage control subsystem, and wherein the first and secondexaminations are performed before the target regular volume and thetarget subvolume are paired and data in the target regular volume iscopied to the target subvolume.
 8. The storage control subsystemaccording to claim 3, wherein the certain host device receives a copyinstruction from the user and issues a copy command in response to thecopy instruction after volume discrimination information for the targetregular volume and volume discrimination information on the targetsubvolume have been inputted by the user and/or issues a recopy commandfor copying once the paired state of the target regular volume andtarget subvolume has been cancelled and the paired state then reformed,and wherein when the storage control subsystem receives the copy commandor recopy command, before executing copy processing on the basis of thecommand, the storage control subsystem performs a first examination byreferencing ON/OFF information corresponding with discriminationinformation on the target subvolume that is included in this command,executing copy processing based on the copy command or recopy commandupon judging that the target subvolume is in the offline state as aresult of the first examination but, on the other hand, executing thesecond examination upon judging that the target subvolume is in theonline state as a result of this first examination.
 9. The storagecontrol subsystem according to claim 3, wherein, instead of or inaddition to performing the second examination, the storage controlsubsystem switches the target subvolume from the online state to theoffline state when it is judged that the target subvolume is in theonline state as a result of the first examination.
 10. The storagecontrol subsystem according to claim 9, wherein the storage controlsubsystem switches the target subvolume from the online state to the offline state in at least one of cases (1) to (3) below: (1) when a settingcancellation command that includes discrimination information on thetarget subvolume is received from the certain host device after thesecond examination result is sent to the certain host device; (2) whenpath group information corresponding with the target subvolume isreferenced, an inquiry is made with regard to whether the connectionthereof with all or part of one or more separate host devices specifiedbased on the path group information may be cancelled, and a replyrelaying that the connection may be cancelled is then obtained inresponse to this inquiry; and (3) when a predetermined time has elapsedafter judging that the target subvolume is in an online state.
 11. Thestorage control subsystem according to claim 3, wherein, when a separatestorage control subsystem is connected to the storage control subsystem,the target regular volume exists in the storage control subsystem andthe target subvolume exists in the separate storage control subsystem,wherein the separate storage control subsystem references the controlmemory in the storage control subsystem, performs the first and secondexaminations, and sends the results of the first and second examinationsto the certain host device.
 12. A storage control subsystem connected toone or more host devices, comprising: a control unit; a plurality oflogical volumes formed on one or more physical storage devices; and acontrol memory in which, for each of the plurality of logical volumes,volume discrimination information, ON/OFF information indicating whetheran online state exists, and, in the event of an online state, path groupinformation with regard to which host device(s) a subvolume is connectedto, are recorded, wherein, as a result of receiving a specific commandfrom a certain host device, the control unit performs, before a targetregular volume and target subvolume among the plurality of volumes arepaired and data in the target regular volume is copied to the targetsubvolume, a first examination of whether the target subvolume is in anonline state on the basis of the ON/OFF information on the targetsubvolume, and, when as a result of this first examination, the targetsubvolume is known to be an online state, the control unit performs asecond examination with regard to which separate host device the targetsubvolume is connected to based on path group information on the targetsubvolume, and wherein the result of the second examination is sent fromthe control unit to the certain host device.